Chapter #21: ATP Synthesis Flashcards
What is the chemiosmotic hypothesis?
Electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane.
What is the proton-motive force?
The unequal distribution of protons is called the proton motive force, and it is composed of two components:
1) A chemical (pH) gradient for the protons
2) A charge gradient due to the unequally distributed, positively charged protons
What does a diagram of the chemiosmotic hypothesis look like?
Describe the structure of ATP synthase - “ball on a stick”
Describe the mechanism of ATP synthase
- Interestingly, ATP formation occurs readily in the absence of proton-motive force.
- The role of the proton gradient is actually to release ATP from the synthase.
- The association of the γ subunit creates three conformations of the β subunit.
- Loose: binds ADP and Pi
- Tight: high affinity for ligands - binds ATP with very high avidity, such that ADP and Pi are converted to ATP
- Open: almost no affinity for ligands - releases bound nucleotide
How to move from one configuration to another one?
Counterclockwise rotation of γ.
- ADP and Pi are transiently combining at the T-form site to form ATP, but the ATP can’t be released.
- A 120o rotation of subunit γ converts the T-form site into an O-form site.
- ATP at the O-form site can now depart.
- The ATP at the O-form site is replaced by ADP and Pi.
The T and L conformations do not release bound nucleotides, only the O conformation allows release.
How does proton flow drive the γ subunit?
*The a subunit abuts the membrane-spanning c units, and appears to contain two hydrophilic half channels where protons can enter, but cannot pass through the entire membrane.
*The a subunit is positioned to interact with two of the c subunits.
*A proton enters the a subunit from the intermembrane space (high H+) of the membrane and binds a specific ASP (or GLU) residue on the associated c subunit.
*The c subunit rotates to a more hydrophobic environment with its now uncharged Asp (or Glu), rotating all the other c subunits with it.
*The c subunit that has rotated all the way around to exposure with the matrix half channel, can release its proton to the proton deficient matrix – deprotonated Asp is regenerated.
What does the ATP synthase mechanism look like on a diagram?
What does the ATP synthase units look like on a diagram?
What is the rotation observed of ATP synthase on a video?
*Only α, β, and γ subunits were used.
*The β subunit was engineered with a his tag that allowed it to be immobilized on a surface.
*The γ subunit was linked to a fluorescently labeled filament. actin
*The addition of ATP revealed rotation as ATP hydrolysis occurred.
How is ATP Synthase Regulated?
- Electrons do not flow through the electron-transport chain unless ADP is available to be converted into ATP (shuttle: ATP-ADP translocase).
- The regulation of oxidative phosphorylation by ADP is called acceptor or respiratory control.
- Acceptor control is an example of control of metabolism by energy charge.
Overall, the process of Oxidative phosphorylation (OXPHOS) is the process of oxidizing nutrients to release energy, which is used generate ATP from ADP and Pi.
What is the fate of mitochondrial ATP?
What is the ATP yield per molecule of glucose?
- Of the 30 molecules of ATP formed by the complete combustion of glucose, 26 are formed in oxidative phosphorylation.
- The metabolism of glucose to two molecules of pyruvate in glycolysis yields the remaining four ATP.
- When glucose undergoes fermentation, only two molecules of ATP are generated per glucose molecule.
Here are the links to review the ETC and ATP synthase
lycolysis, the TCA cycle and Cellular Respiration”
https://www.youtube.com/watch?v=_SkPwVO9BFI
“Cellular Respiration (ETC)”
https://www.youtube.com/watch?v=LQmTKxI4Wn4&list=PLltdM60MtzxM6jjoW6mRxYuGzZoSWDYwe
“Molecular animation of ATP synthase”
https://www.youtube.com/watch?v=kXpzp4RDGJ
